We propose to extend the studies of porphyrins and of hemoproteins by XPS. In particular, we propose the study of porphyrins in the vapor, studying both core and valence levels. To this end, we have constructed a small oven which fits into our spectrometer. Gas phase core level studies will allow the measurement of carbon ls binding energies, thus will lead to a better idea of the charge distribution in the compounds. The valence level measurements contribute primarily to our understanding of the placement of the levels of the compound derived from metal d levels. We propose also to study the Fe core binding energies in compounds of horseradish peroxidase. We expect to attempt to bind the protein directly to a film cast on the probe. If this fails, we must turn to frozen solutions. Finally, we propose to evaluate the ability of semiempirical molecular orbital theory to duplicate the valence-level XPS spectra of various metalloporphyrins, measured by us.